1. Field of the Invention
The present invention relates to a rotor of a rotary electric machine, the rotor having a commutator surface facing an axial rear end of the rotary machine.
2. Description of Related Art
Recently, improvement of fuel economy in an automobile vehicle is becoming an important subject in order to prevent temperature rise on the earth. For this purpose, engine improvement has been done very eagerly. It is also important to make a starter motor small in size and light in weight since the starter motor is one of major auxiliary equipment mounted on the engine. For this end, a starter motor utilizing rear end portions of conductor segments as a commutator surface has been proposed in JP-B2-2924605. According to the proposed structure, it is not necessary to provide an independent commutator. Therefore, it is possible to considerably reduce the size and weight of the starter motor. In addition, this structure eliminates a process of undercutting the commutator surface, resulting in reduction of manufacturing cost.
In the proposed structure, however, the thickness of each rear end portion of the conductor segment in the axial direction is uniformly made throughout its entire radial length while its width on the commutator surface gradually decreases from the radial outside toward the radial inside. As a result, the cross-sectional area of the rear end portion of the conductor segment gradually decreases from the radial outside toward the radial inside. Therefore, electrical resistance of an armature coil constituted by such plural conductor segments becomes high, and accordingly the output of the starter motor is somewhat sacrificed. Further, an upsetting process is required to form the conductor segment having such a rear end portion from a conductor wire. Therefore, the process of forming the conductor segment is not easy, resulting in high manufacturing cost.